U.S. patent application number 11/085153 was filed with the patent office on 2005-10-06 for apparatus for current measurement.
Invention is credited to Ludwig, Klaus, Rieger, Gotthard.
Application Number | 20050218882 11/085153 |
Document ID | / |
Family ID | 34862929 |
Filed Date | 2005-10-06 |
United States Patent
Application |
20050218882 |
Kind Code |
A1 |
Ludwig, Klaus ; et
al. |
October 6, 2005 |
Apparatus for current measurement
Abstract
The apparatus for measurement of a current which is flowing in
an axially elongated electrical conductor at a first electrical
potential. The apparatus contains at least one associated sensor
element associated with the conductor that is electrically isolated
from it at a second electrical potential different from the first
electrical potential of the electrical conductor, and having
magnetoresistive characteristics. The sensor element is intended to
form a loop which is magnetically closed around the conductor in
the circumferential direction, with the resistance value being
tapped off at axially opposite ends. Its magnetoresistive part is
preferably composed of a non-metallic powder composite material
with a high magnetoresistive effect.
Inventors: |
Ludwig, Klaus; (Erlangen,
DE) ; Rieger, Gotthard; (Erlangen, DE) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O.BOX 8910
RESTON
VA
20195
US
|
Family ID: |
34862929 |
Appl. No.: |
11/085153 |
Filed: |
March 22, 2005 |
Current U.S.
Class: |
324/117R |
Current CPC
Class: |
G01R 15/205
20130101 |
Class at
Publication: |
324/117.00R |
International
Class: |
G01R 033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 23, 2004 |
DE |
10 2004 014 212.2 |
Dec 23, 2004 |
DE |
10 2004 062 474.7 |
Claims
What is claimed is:
1. An apparatus for measurement of a conductor current which is
flowing in an axially elongated electrical conductor at a first
electrical potential, comprising: at least one sensor element,
associated with the conductor that is electrically isolated from it
at a second electrical potential different from the first
electrical potential of the electrical conductor and having
magnetoresistive characteristics; and means for tapping off the
resistance value, dependent on the magnetic field of the current,
across the element and for further processing of this value,
wherein the at least one sensor element which is formed from
magnetoresistive material forms a loop which is magnetically closed
around the conductor in the circumferential direction and has a
predetermined axial extent and wherein the resistance value is
tapped off axially at opposite ends of the sensor element.
2. The apparatus as claimed in claim 1, wherein the axial extent is
at least 1 mm.
3. The apparatus as claimed in claim 1, wherein the
magnetoresistive part of the sensor element is formed from a
metallic or non-metallic material.
4. The apparatus as claimed in claim 3, wherein the metallic
material is of the AMR type.
5. The apparatus as claimed in claim 3, wherein the non-metallic
material is a powder material with a high magnetoresistive
effect.
6. The apparatus as claimed in claim 5, wherein the powder
composite material contains particles composed of at least one
Heusler or half-Heusler phase, to which a small proportion of at
least one oxide material is added.
7. The apparatus as claimed in claim 6, wherein the proportion of
the oxide material in the powder composite material is less than
25% by volume.
8. The apparatus as claimed in claim 6, wherein a chromium or
aluminum oxide is chosen as the oxide material.
9. The apparatus as claimed in claim 5, wherein the powder material
contains particles composed of at least one manganese Perovskite
phase.
10. The apparatus as claimed in claim 9, wherein the powder
material is a composite material to which a small proportion of an
organic material is added.
11. The apparatus as claimed in claim 10, wherein the proportion of
the organic material in the powder composite material is less than
25% by volume.
12. The apparatus as claimed in claim 10, wherein a polymer is
chosen as the organic material.
13. The apparatus as claimed in claim 1, wherein the magnetically
closed loop is formed by the sensor element being in the form of a
ring or sleeve.
14. The apparatus as claimed in claim 1, wherein at least two
sensor elements are arranged one behind the other in the axial
longitudinal direction of the conductor.
15. The apparatus as claimed in claim 14, wherein the sensor
elements are connected to form at least one of a full bridge and a
partial bridge, with the preferred directions of the magnetizations
being in opposite directions from one element to the next.
16. The apparatus as claimed in claim 1, wherein the at least one
sensor element is subdivided into at least two partial elements,
arranged distributed in the circumferential direction around the
conductor.
17. The apparatus as claimed in claim 15, wherein the partial
elements are connected to form at least one of a full bridge and a
partial bridge, with the preferred directions of the magnetizations
being in opposite directions from one partial element to the
next.
18. The apparatus as claimed in claim 1, wherein the at least one
sensor element is provided with a high-permeability shielding
sleeve.
19. The apparatus as claimed in claim 2, wherein the
magnetoresistive part of the sensor element is formed from a
metallic or non-metallic material.
20. The apparatus as claimed in claim 3, wherein the non-metallic
material is a powder composite material, with a high
magnetoresistive effect.
21. The apparatus as claimed in claim 7, wherein a chromium or
aluminum oxide is chosen as the oxide material.
22. The apparatus as claimed in claim 11, wherein a polymer is
chosen as the organic material.
Description
[0001] The present application hereby claims priority under 35
U.S.C. .sctn.119 on German patent application numbers DE 10 2004
014 212.2 filed Mar. 23, 2004 and DE 10 2004 062 474.7 filed on
Dec. 23, 2004, the entire contents of which are hereby incorporated
herein by reference.
FIELD OF THE INVENTION
[0002] The invention generally relates to an apparatus for
measurement of a conductor current which is flowing in an axially
elongated electrical conductor at a first electrical potential.
Preferably, it relates to one having at least one sensor element
which is associated with the conductor that is electrically
isolated from it and has magnetoresistive characteristics, and
having a device for tapping off the resistance value, which is
dependent on the magnetic field of the current, across the element
and for further processing of this value.
BACKGROUND OF THE INVENTION
[0003] An apparatus for measurement of a conductor current which is
flowing in an axially elongated electrical conductor at a first
electrical potential is generally disclosed in WO 95/09447 A.
[0004] Current measurement is used throughout the entire field of
electrical power transmission, power management, control
engineering and automation engineering. Since this frequently
relates to a safety-relevant function, the current transformer that
is used must be protected against external disturbance influences
and fields. If low-cost and geometrically simple solutions are
available, the current monitoring can intervene at an early stage,
and can prevent damage, at a large number of points.
[0005] Nowadays, various solutions exist for current detection and
measurement, for example with measurement resistors (shunts) being
used combined with opto couplers, as well as current transformers,
Hall elements, field plates, sensor systems using magnetoresistive
material, and fiber-optic current measurement devices. However,
many of the current sensors have a limited operating range and are
limited, for example by alternating-current measurement since they
are based on inductive principles, or cannot be integrated. One
problem of the magnetic solutions which have been mentioned, in
which the field of a conductor through which a current passes is
measured, results from the fact that a disturbance field frequently
acts highly directly, and shielding devices or graded and/or
compensation methods must be used all the time.
[0006] The WO-A document which was cited initially discloses a
current measurement apparatus which has at least one sensor element
which surrounds a conductor through which current flows, in the
form of an open ring. In this case, the open ring is formed by a
multilayer system composed of metallic magnetoresistive material of
the so-called AMR (Anisotropic Magneto Resistance) type. The
magnetoresistive material is made contact with at the adjacent ends
of this ring, which form a slot, in order to tap off the resistance
value. A sensor element such as this may be connected to further
elements which are not sensitive to magnetic fields, to form a
bridge. The magnetoresistive materials which are used can be
produced in curved shapes, such as the slotted annulus that is
required, only with considerable effort.
[0007] DE 39 29 452 A1 likewise discloses a current measurement
apparatus. The known apparatus contains a magnetic field ring
sensor, which has a substrate with a central circular opening for
an electrical conductor to pass through. A large number of
individual sensor elements of the so-called barber pole type are
arranged around the circular opening and each have strips which are
deposited on the substrate using a thin-film technique, are aligned
radially, are composed of magnetoresistive material and have
electrical conductor parts running at an angle to them. The
individual sensor elements, which are considerably separated from
one another in the circumferential direction, are electrically
connected in series. The design of this known apparatus is highly
complex.
SUMMARY OF THE INVENTION
[0008] An object of an embodiment of the present invention is to
refine the known current measurement apparatuses so as to simplify
their design for adequate sensitivity.
[0009] According to an embodiment of the invention, at least one
sensor element which is formed from magnetoresistive material is
accordingly intended to form a loop which is magnetically closed
around the conductor in the circumferential direction and has a
predetermined axial extent, with the resistance value being
intended to be tapped off at axially opposite ends of the sensor
element.
[0010] This refinement of the current measurement apparatus
advantageously makes it possible to design its at least one current
sensor element in a simple manner: A loop which is magnetically
virtually completely closed, in particular in the form of a ring or
sleeve, and composed of metallic or, in particular, non-metallic
magnetoresistive material is located in the magnetic field circuit
of the current-carrying electrical conductor, and is conductively
isolated from it by a thin insulation layer. This loop has a
predetermined, pronouncedly axial extent, which is considerably
greater than the thickness of the magnetoresistive thin films, and,
in particular, is at least 1 mm.
[0011] In consequence, a closed magnetic flux can be produced in
the magnetically closed loop, highly effectively making use of the
rotationally symmetrical field of the conductor for magnetization
of the magnetoresistive material. Thus, it can achieve a
correspondingly high magnetoresistive effect or output signal
without any need for special additional electrically conductive
elements as in the case of magnetoresistive sensor elements of the
barber pole type. The influence of homogeneously superimposed
fields such as disturbance fields is in this case advantageously
small. Both the manufacture of appropriate loops and the process of
making contact with them at the axially opposite ends of their
magnetoresistive material are particularly simple.
[0012] Advantageous refinements of the current measurement
apparatus according to the invention are described in the example
embodiments. Accordingly, the following features can additionally
also be provided for the current measurement apparatus:
[0013] a material which indicates an AMR effect can be provided as
a metallic material for the magnetoresistive part of the sensor
element, in which case the magnetoresistive part can be designed
using known methods.
[0014] instead of this, a powder material with a high
magnetoresistive effect can preferably be used as a non-metallic
material. In this context, the expression a high magnetoresistive
effect refers to a value defined in the normal manner of at least
3% at room temperature. In this case, a powder composite material
may advantageously be chosen as the powder material, which
expression includes a composition of at least two different
materials in which a particle structure can still be found. The
material can be produced and processed in a known manner. Composite
materials such as these include, in particular, the so-called
Colossal-Magneto-Resistance (CMR)--or Tunnel-Magneto-Resistance
(TMR) materials (see, for example, the brochure "XMR-Technologien
(Technologieanaly-se- Magnetis-mus Band 2)" [XMR technologies
(Technological analysis--magnetism Volume 2] from the
VDI-Technologiezentrum "Physikalische Technologien" [Physical
Technologies VDI Technology Center], Dusseldorf, (DE), 1997, pages
26 to 27 and 37 to 43). These advantageously allow any desired 3D
shape. Since, furthermore, these materials have a soft-magnetic
behavior, the magnetic flux which is produced can be carried very
well by them.
[0015] one powder composite material which is particularly suitable
contains particles composed of at least one Heusler or half-Heusler
phase, to which a small proportion of at least one oxide material,
preferably less than 25% by volume, is added.
[0016] instead of this, the powder material may contain particles
composed of at least one manganese perovskite phase to which, if
required, a small proportion of an organic material is added in
order to form a composite material. The added proportion in the
powder composite material may also in this case advantageously be
less than 25% by volume. These materials make it possible to form
highly magnetoresistive composite materials with adequate
flexibility.
[0017] the current measurement apparatus may, of course, have two
or more sensor elements, which are arranged one behind the other in
the axial longitudinal direction of the conductor. In this case,
the preferred directions (which point in the axial longitudinal
direction) of the magnetization can advantageously be in opposite
directions from one element to the next. Elements such as these can
then easily be connected to form a full bridge or partial bridge.
It is thus possible, for example, to compensate for temperature
influences on the individual sensor elements to a major extent.
[0018] furthermore or instead of this, the at least one sensor
element can be subdivided into two or more partial elements, in
particular with the partial elements being arranged distributed in
the circumferential direction around the conductor. A design such
as this on the one hand makes it easier to fit the element around
an electrical conductor. On the other hand, a full bridge or
partial bridge can also be formed in this case, in which case the
preferred directions of the magnetization of adjacent partial
elements should likewise be set such that they are aligned parallel
and in opposite directions.
[0019] furthermore, it can be regarded as being particularly
advantageous for the at least one sensor element to be provided
with a high permeability shielding sheath. The combination of the
sensor element with a sheath such as this allows very effective
shielding. Furthermore, this results in a current sensor which, for
example, can easily be integrated in the insulation of a power
cable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Further advantageous refinements of the current measurement
apparatus according to the invention are described in the example
embodiments below, and are illustrated in the drawings.
[0021] The invention will be explained in more detail in the
following text using preferred exemplary embodiments of measurement
apparatuses and with reference to the drawings. In the figures of
the drawing, which are in the form of slightly schematic
illustrations,
[0022] FIG. 1 shows an oblique view of a measurement apparatus such
as this having a single sensor element,
[0023] FIG. 2 shows a side view of another embodiment of a
measurement apparatus having a half bridge or full bridge composed
of two or more connected sensor elements,
[0024] FIG. 3 shows a cross-sectional view of a further embodiment
of a measurement apparatus having a full bridge composed of sensor
partial elements,
[0025] FIGS. 4 and 5 show side views of the measurement apparatuses
shown in FIG. 1 and FIG. 2, respectively, each with a shielding
sheath, and
[0026] FIG. 6 shows an end view of the measurement apparatus shown
in FIG. 4.
[0027] In this case, corresponding parts in the figures are in each
case provided with the same reference symbols.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0028] The current measurement apparatus 2 which is illustrated
according to an embodiment of the invention, as illustrated in FIG.
1, has a sensor element 3 which surrounds an electrical conductor 4
through which direct current or alternating current I is flowing.
In this case, the sensor element 3 is conductively isolated from
the electrical conductor 4, for example being isolated from it by
way of a thin insulation layer 5.
[0029] The sensor element is in particular in the form of a ring or
sleeve, which represents a sheath which magnetically completely
surrounds the electrical conductor 4 in the circumferential
direction. In this case, the sensor element has a predetermined
extent which is pronounced in the axial direction and shall be at
least 1 mm. At least a substantial proportion of it is composed of
a magnetoresistive material.
[0030] Fundamentally, all materials which are known per se with an
XMR effect (see the cited brochure "XMR Technologies", pages 11 to
43) may be used for this purpose. In this case, the
magnetoresistive part of the sensor element 3 may be formed from a
metallic or non-metallic material using known methods. By way of
example, a metallic thick-film or in particular thin film composed
of an AMR material may thus be provided.
[0031] A non-metallic powder material is particularly suitable, in
particular a powder composite material which indicates a high
magnetoresistive effect of at least 3% (based on the normal
definition). The material can be formed using, in particular,
methods which are known from powder processing technology, in which
case a carrier can also be applied. It is thus possible, for
example, to use sintering, molding, spraying/injection, thick film
or thin film, slip/paste or print methods.
[0032] A non-metallic powder composite material with a high CMR or
TMR effect has been chosen for the exemplary embodiments in the
following text. This material has particles or powder composed of
at least one magnetoresistive, or possibly even
non-magnetoresistive, material, with the proportion of this
material advantageously being chosen to be very high and, for
example, being more than 75% by volume. The remaining proportion is
made up from at least one further material, in particular such as
an oxide or organic material, in which case the magnetoresistive
characteristics may possibly be produced only with this
additive.
[0033] One preferred example of a highly magnetoresistive powder
composite material such as this in particular uses powder particles
with Heusler or half-Heusler phases as the main component. This is
primarily because it is known that powder composite materials with
a high magnetoresistive TMR effect can be produced using powders
composed of these initially virtually non-magnetoresistive
materials, in conjunction with a small amount of an oxide material
which acts as a grain boundary form means (see, for example,
dissertation by Thomas Block: "Neue Materialien fur die
Magnetoelektronik: Heusler- und Halb-Heusler-Phasen" [Novel
materials for magneto electronics: Heusler and half-Heusler
phases], Johannes Guttenberg University, Mainz, 2000, in particular
the section entitled "Komposit-Material" [composite material], on
pages 159 to 177). In this case, the following alloys, in
particular, may be used:
[0034] CoV.sub.1-xMn.sub.xSb
[0035] Co.sub.2CrAl
[0036] Co.sub.2Cr.sub.0,6Fe.sub.0,4Al
[0037] Co.sub.2Cr.sub.0,6Fe.sub.0,4Ga
[0038] In this case, individual components of the abovementioned
materials may be substituted in a known manner by other components
in which case two or more substituents may also replace one
component.
[0039] Non-magnetic materials, in particular oxides such as
Cr.sub.2O.sub.3 or Al.sub.2O.sub.3, may be used as additional
materials for the abovementioned main component powders. The
important factor in this case is that these materials form grain
boundaries in the composite material, which are a precondition for
a TMR effect.
[0040] Manganese Perovskite materials are also particularly
suitable owing to the CMR effect which occurs in this substance
group. Corresponding known Perovskites are in particular chosen
from the Ln.sub.1-xA.sub.xMnO.sub.3+d system, an alkaline earth
metal being chosen as the A component (see, for example, DE 43 10
318 C2). The structure and the physical characteristics of such
Perovskites are governed to a major extent not only by the
composition but also by the stoichiometry of the oxygen index d,
which can be set in a known manner by suitable choice of the
temperature and of the oxygen partial pressure.
[0041] It is also known that highly magnetoresistive elements with
a good shaping capability can be produced using these materials by
adding small proportions of organic material, in particular such as
polymer materials (see, for example, the article by S. Barth:
"LSMO-Siebdruckschichten fur CMR-Anwendungen" [LSMO screen-printing
layers for CMR applications] during the symposium entitled
"Magnetoresistive Sensoren VI: Grundlagen, Herstellung, Anwendung",
[Magnetoresistive sensors, VI: Fundamentals, Production, Use],
Wetzlar (DE), Mar. 13 and 14 2001). In this case as well, the added
proportion is generally less than 25% by volume.
[0042] The insulated conductor 4 through which current flows
produces a magnetic field of strength of H which leads in the
tubular, magnetoresistive sleeve of the sensor element 3 to a
resistance value R which depends on the field strength H and on the
current I. This resistance value is in this case advantageously
tapped off at the axially opposite ends 7a and 7b of the sensor
element 3 or of its magnetoresistive sleeve, by passing
predetermined measurement current i.sub.meas in the axial direction
through the magnetoresistive material of the sensor element. The
measurement voltage, which is correlated to the resistance value,
is then processed further in a known manner.
[0043] As is shown in the illustration in FIG. 2, a current
measurement apparatus 10 may, of course, also have two or more
sensor elements 3a to 3d, which are arranged one behind the other
in the axial direction of the conductor 4. These elements can
advantageously be connected to form a half bridge or full bridge.
For this purpose, preferred directions of the magnetizations
m.sub.a to m.sub.d in the individual elements are preferably set
such that they point in the longitudinal direction and are at the
same time in opposite directions from one element to the next.
[0044] The embodiments shown in FIGS. 1 and 2 have been based on
the assumption that the at least one sensor element has at least
one sleeve, which is completely closed in the circumferential
direction and is composed of highly magnetoresistive composite
material. However, since all that matters is to form a closed
magnetic ring around the electrical conductor in the
circumferential direction, the sleeve or ring which is used can if
required also be subdivided into partial elements which are
longitudinally electrically insulated but are electrically
connected to one another at the ends.
[0045] FIG. 3 shows a corresponding embodiment of a current
measurement apparatus 11 having a sensor element 13 which is formed
from four quarter shell elements 13a to 13d which are located
distributed alongside one another in the circumferential direction.
In this case, the air gaps between adjacent partial elements should
be kept as small as possible. In this case as well, the partial
elements can be connected to form a full bridge in order to
compensate for temperature influences and disturbance fields
aligned transversely with respect to the conductor.
[0046] In this case, the preferred directions (which point in the
longitudinal direction) of the magnetizations m.sub.a to m.sub.d
should be in opposite directions in the circumferential direction
from one partial element to the next. Partial bridges can also be
formed by way of partial elements such as these. If required, it is
possible to combine the individual sensor elements, as shown in
FIG. 2, with assembled sensor elements 13 as shown in FIG. 3.
[0047] As can be seen from FIGS. 4 and 5, the embodiments shown in
FIGS. 1 to 3 in the case of a current measurement apparatus 14 or
14' may additionally be surrounded by a shielding sheath 15 in
order to effectively suppress disturbance fields. In this case, a
sensor element 13 as shown in FIG. 3 is assumed to be provided for
the current measurement apparatus 14 shown in FIG. 4, while the
current measurement apparatus 14' in FIG. 5 is equipped with four
sensor elements 3a and 3d as shown in FIG. 2. The shielding sheath
15 is at a distance from and is isolated from the magnetoresistive
parts which are surrounded by it. Those parts which are in each
case concealed by the shielding sheath 15 in the side views shown
in FIGS. 4 and 5 are indicated by dashed lines.
[0048] FIG. 6 shows the current measurement apparatus 14 from FIG.
4 in a view equivalent to a plan view of one end of the
apparatus.
[0049] The following text provides two estimates of the disturbance
influence of homogeneously superimposed fields on a
magnetoresistive ring or a sleeve based on the assumption of a
linear magnetoresistive effect. In this case, reference should be
made to the embodiments of current measurement apparatuses shown in
FIGS. 1 and 2:
[0050] 1) If the sleeve 3 is magnetized in a rotationally
symmetrical form by a current flow I, a uniform magnetoresistive
effect is produced throughout the entire annular area. If the
conductor 4 with the magnetoresistive sleeve 3 is located in a
homogeneous disturbance field, the resultant field is attenuated on
one side of the sleeve by superimposition of the conductor field H
and the disturbance field. On the opposite side of the conductor,
and thus of the sleeve, the field is, however, increased for the
same reasons. Owing to the symmetry of the arrangement, an
equivalent circuit with two parallel-connected resistors R.sub.0
can be assumed for the sleeve. Therefore, this results in the
following overall resistance R based on the relationship: 1 1 R = 1
R 0 + 1 R 0 = 2 R 0 , thatistosay R = R 0 2 .
[0051] 2) The symmetry of the rotationally symmetrical
magnetization with a closed flux is interrupted by a homogeneously
superimposed disturbance field. A different magnetoresistive effect
then occurs in opposite halves of the sleeve 3. A simplified
equivalent circuit can thus be produced for the sleeve with two
parallel-connected resistors (R.sub.0+R.sub.st), where R.sub.st is
intended to represent the resistance connected to the superimposed
disturbance field. This then results in the following relationship:
2 1 R = 1 R 0 + R st + 1 R 0 - R st = 2 R 0 R 0 - R st 2 ,
[0052] that is to say 3 R = R 0 2 - [ 1 2 R st 2 R 0 ] .
[0053] In this situation, the linear disturbance in the
magnetization of the two parallel-connected paths is admittedly not
compensated for completely as in case 1) of a series arrangement;
however, it is evident in the magnetoresistive effect only as a
second-order disturbance, and is therefore of secondary
importance.
[0054] However, it is evident from both estimates that the use
according to the invention of a loop which is magnetically
completely closed in the circumferential direction as a sensor
element in the rotationally symmetrical field of the conductor
results in disturbance fields having only a relatively minor
influence. The current measurement apparatus designed according to
the invention thus provides a universal sensor solution, which can
easily be integrated, for monitoring and detection of both DC and
AC currents.
[0055] Exemplary embodiments being thus described, it will be
obvious that the same may be varied in many ways. Such variations
are not to be regarded as a departure from the spirit and scope of
the present invention, and all such modifications as would be
obvious to one skilled in the art are intended to be included
within the scope of the following claims.
* * * * *